virtio: force vring descriptors to be allocated from lowmem

Virtio devices may attempt to add descriptors to a virtqueue from atomic
context using GFP_ATOMIC allocation. This is problematic because such
allocations can fall outside of the lowmem mapping, causing virt_to_phys
to report bogus physical addresses which are subsequently passed to
userspace via the buffers for the virtual device.

This patch masks out __GFP_HIGH and __GFP_HIGHMEM from the requested
flags when allocating descriptors for a virtqueue. If an atomic
allocation is requested and later fails, we will return -ENOSPC which
will be handled by the driver.

Cc: stable@kernel.org
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index e639584b2dbd..286c30cb393d 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -135,6 +135,13 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
         unsigned head;
         int i;
 
+        /*
+         * We require lowmem mappings for the descriptors because
+         * otherwise virt_to_phys will give us bogus addresses in the
+         * virtqueue.
+         */
+        gfp &= ~(__GFP_HIGHMEM | __GFP_HIGH);
+
         desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
         if (!desc)
                 return -ENOMEM;